Method for producing In2O3—SnO2 precursor sol

ABSTRACT

The invention relates to a method for forming a transparent conductive thin film of In 2 O 3 —SnO 2  on a surface of a plastics substrate of less heat resistance other than that of glass, ceramics, etc. When an In 2 O 3 —SnO 2  precursor sol is produced by hydrolyzing and polymerizing a solution containing indium alkoxide and tin alkoxide, either tri-s-butoxyindium or tri-t-butoxyindium is used as the indium alkoxide. Water is added to the solution containing indium alkoxide and tin alkoxide at a temperature of not higher than −20° C. The obtained In 2 O 3 —SnO 2  precursor sol is applied to a surface of a substrate to form a gel film, then the gel film is either irradiated with an ultraviolet beam of which wave length is not longer than 360 nm, or irradiated with an ultraviolet beam of which wave length is not longer than 260 nm and further irradiated with a laser beam of which wave length is not longer than 360 nm, to crystallize the gel forming the thin film, whereby an In 2 O 3 —SnO 2  thin film having a conductivity is formed on the surface of the substrate.

TECHNICAL FIELD

The present invention relates to a method for producing an In₂O₃—SnO₂precursor sol used for forming a transparent conductive thin film ofindium oxide-tin oxide In₂O₃—SnO₂ (ITO) on a surface of a substrate ofglass, ceramics, plastics, etc., and to a method for producingIn₂O₃—SnO₂ thin film.

BACKGROUND ART

To form a thin film of a metal oxide on a substrate utilizing a sol-gelmethod, a metallic alkoxide is used as a raw material, and a precursorsol of the metal oxide is prepared by hydrolyzing and polymerizing themetallicalkoxide. The sol thus obtained is then applied to the surfaceof the substrate, and after forming a gel of the metal oxide on thesurface of the substrate, a film of the gel is subject to a heattreatment at an appropriate temperature. At the time of forming anIn₂O₃—SnO₂ thin film on the surface of the substrate utilizing a sol-gelmethod, indium alkoxide and tin alkoxide are used as starter material.

Generally, as the hydrolysis of the metallic alkoxide such as indiumalkoxide, tin alkoxide, etc. takes place very quickly, it is difficultto prepare a homogeneous sol capable of achieving a homogeneous filmformation. To cope with this, there is a method in which concentrationof metallic alkoxide is extremely reduced to restrain the speed ofhydrolysis of the metallic alkoxide. By employing such a method, it iscertainly possible to achieve a film formation of homogeneous sol.However, in such a method, thickness of the thin film obtained by onefilm formation process becomes extremely small, and this method is notsuited for practical use.

As mentioned above, when concentration of the metallic alkoxide is high,it is difficult to prepare any homogeneous sol from which a homogeneousfilm can be formed. On the other hand, when concentration of themetallic alkoxide is reduced to make it possible to form a homogeneousfilm, thickness of the thin film obtained by one film formation processis excessively small, which is not suited for practical use. Moreover,generally, the sol obtained by hydrolyzing the metallic alkoxide isunstable such that change in viscosity may occur, precipitate may beproduced, or gelation takes place, due to storage for a long time. Theseproblems occur in the same manner at the time of forming the In₂O₃—SnO₂thin film utilizing a sol-gel method in which indium alkoxide and tinalkoxide are used as starter material.

As a further method for obtaining a sol from which a film is formedwhile increasing the concentration of metallic alkoxide and restrainingthe speed of hydrolysis, several attempts for stabilizing the metallicalkoxide by adding some organic compound capable of being multidentatehave been heretofore proposed. For example, it was reported that in theformation of an alumina thin film using aluminum-s-butoxide as a startermaterial, β-diketone is effective (Article 97,396(1989) by JapanCeramics Association), and that in the formation of a titania thin filmusing titanisopropoxide as a starter material, 1,3-butanediol iseffective (Article by Dr. Hisao Koshiba of Toyohashi Technological andScientific College, March, 1993), diethanol amine is effective (Article23, 2259 (1988) by Journal of Materials Science), and β-diketone iseffective (Article 97,213(1989) by Japan Ceramics Association) It isalso reported that in the formation of a zirconia thin film usingzirconium-n-butoxide as a starter material, employment of diethyleneglycol is effective (Article 95,942(1987) by Ceramic IndustryAssociation). Further, it was reported in the Articles 74,1407(1991) byJournal of American Ceramics Society and 25, 3960 (1990) by Journal ofMaterials Science that employment of β-diketone and alkanol amine iseffective in the composition of a composite oxide such as PbTiO₃ andPb(Zr, Ti)O₃.

In the Physics of Tin Film, 5, p87(1969) and in the Academic Press, amethod for producing an oxide film utilizing hydrolysis of variousinorganic salts such as chloride, sulfate, nitride, ammonium salt andaqua-complex was reported. Further, it was disclosed in the Article102,200(1994) by Japan Ceramics Association that, to prepare In₂O₃—SnO₂sol being a composite oxide, indium nitrate and tin chloride are usedinstead of metallic alkoxide.

However, in the method for restraining the speed of hydrolysis of themetallic alkoxide by stabilizing the metallic alkoxide such as indiumalkoxide, tin alkoxide, etc. by adding some multidentate compound, it iscertainly possible to prepare easily a homogeneous sol suited for filmformation, but a lot of organic substances of high boiling pointdifficult to be decomposed at a high temperature exist in the sol or gelfilm. As a result, to remove such organic substances, it is necessaryfor the gel film to be heat-treated at a high temperature of about 500°C. Further, since a lot of organic substances exist in the gel film,when heat-treating the gel film, reduction in weight of the film islarge. In other words, a large number of pores are produced as theresult of removing the organic substances from the gel film, whicheventually results in any defect of the obtained thin film of metaloxide such as In₂O₃—SnO₂. Moreover, to remove the pores in the film, anadditional energy is required for elaboration of the thin film and,therefore, to obtain an In₂O₃—SnO₂ thin film having desiredcharacteristics, a burning at a temperature of not lower than 600° C. isusually required.

Furthermore, any of the mentioned methods utilizing a metallic salt isessentially a thermal decomposition method, and therefore a lot ofproblems may occur in the aspect of film quality after the heattreatment.

DISCLOSURE OF THE INVENTION

The present Invention was made in view of the above-discussed problemsand has an object of providing a method for producing an In₂O₃—SnO₂precursor sol capable of being highly concentrated, preferable information of a film, and superior in stability. Another object of theinvention is, by using such a precursor sol, to provide a method forproducing an In₂O₃—SnO₂ thin film capable of crystallizing In₂O₃—SnO₂ ata low temperature and having a characteristic superior in low resistancevalue (high conductivity), and which method enables a thin film to beformed on a substrate of low heat resistance such as plastics.

In order to accomplish the foregoing objects, the first inventionprovides a method for producing an In₂O₃—SnO₂ precursor sol byhydrolyzing and polymerizing a solution containing indium alkoxide andtin alkoxide, characterized in that either tri-s-butoxyindium ortri-t-butoxyindium is used as said indium alkoxide.

In this respect, as the indium alkoxide and tin alkoxide both serving asstarter material for preparing the In₂O₃—SnO₂ precursor sol are stronglyassociated with each other, characteristics of the obtained precursorsol are different depending upon the combination of compounds. In caseof the production method according to the first invention of thementioned composition, among the starter materials, eithertri-s-butoxyindium or tri-t-butoxyindium is used as the indium alkoxide,and these indium alkoxides respectively have an alkoxyl group of largesteric hindrance, and their degree of association is small. Accordingly,formation of complex salt between tri-s-butoxyindium ortri-t-butoxyindium and tin alkoxide proceeds easily. As a result, itbecomes possible to obtain an In₂O₃—SnO₂ precursor sol which is stablewithout occurrence of any change in viscosity, formation of precipitateand gelation in spite of storage for a long time, superior inwettability, capable of being formed into a homogeneous film in the air,and capable of being concentrated such that concentration by 2 weightpercent or more is achieved in terms of concentration of oxide whilekeeping the mentioned stability and film formation characteristic.

Accordingly, in the production method according to the first invention,it is possible to prepare an In₂O₃—SnO₂ precursor sol of highconcentration which is superior in stability and film formationcharacteristic, and by using this precursor sol, it is further possibleto obtain a homogeneous In₂O₃—SnO₂ thin film having a desired thickness.

In the production method of above composition according to the firstinvention, it is possible to use either one butoxytin as the tinalkoxide serving as a starter material and which is selected from thegroup consisting of tetra-n-butoxytin, tetra-s-butoxytin andtetra-t-butoxytin, or two or more of them combined with each other. Inthis case, it is possible to obtain an In₂O₃—SnO₂ precursor sol capableof being more highly concentrated, which is superior in stability andfilm formation characteristic.

In the production method of above composition according to the firstinvention, it is possible that acid amide of 5 weight % or more inconcentration is included in the solution containing indium alkoxide andtin alkoxide. In this case, the alkoxide is stabilized by coordinationof small acid amide in the alkoxide, and as a result of this, ahomogeneous In₂O₃—SnO₂ precursor sol is obtained, and with its filmformation characteristic improved, an In₂O₃—SnO₂ precursor sol fromwhich a more homogeneous film is formed can be obtained.

In order to accomplish the foregoing objects, the second inventionprovides a method for producing an In₂O₃—SnO₂ precursor sol byhydrolyzing and polymerizing a solution containing indium alkoxide andtin alkoxide, characterized in that water is added to the solutioncontaining indium alkoxide and tin alkoxide at a temperature of nothigher than −20° C.

In the production method of above composition according to the secondinvention, by performing the addition of water to the solutioncontaining indium alkoxide and tin alkoxide at a temperature of nothigher than −20° C., speed of the hydrolysis and polymerization ofindium alkoxide and tin alkoxide is restrained, and therefore ahomogeneous In₂O₃—SnO₂ precursor sol from which a homogeneous film isformed can be obtained.

Accordingly, in the production method according to the second invention,it is possible to prepare a homogeneous In₂O₃—SnO₂ precursor sol of highconcentration from which a homogeneous film of high concentration can beformed and in which amount of organic substance remains less in the gelfilm after the film formation. The precursor sol thus obtained isoptimum for the formation of In₂O₃—SnO₂ thin film, and it becomespossible to obtain an In₂O₃—SnO₂ thin film of high quality from thisprecursor sol.

In the production method of above composition according to the secondinvention, it is possible to hydrolyze and polymerize the solutioncontaining indium alkoxide and tin alkoxide without using anymultidentate compound. In this manner, as a result of not using anymultidentate compound, when a film has been formed using the In₂O₃—SnO₂precursor sol, amount of organic substance remains less in the gel film.

In the production method of above composition according to the secondinvention, it is preferable that the addition of water to the solutioncontaining indium alkoxide and tin alkoxide is performed within thetemperature range of −50° C. to −80° C.

The third invention provides a production method characterized in thatthe In₂O₃—SnO₂ precursor sol obtained by the production method accordingto the mentioned first or second invention is applied to a surface of asubstrate, a thin film of In₂O₃—SnO₂ gel capable of being crystallizedby heat treatment at a temperature of not higher than 300° C. is formedon the surface of the substrate, then the thin film is irradiated withan ultraviolet beam of which wave length is not longer than 360 nm tocrystallize the In₂O₃—SnO₂ gel forming the thin film, whereby anIn₂O₃—SnO₂ thin film having a conductivity is formed on the surface ofthe substrate.

In the production method of above composition according to the thirdinvention, by applying the In₂O₃—SnO₂ precursor sol obtained by theproduction method according to the mentioned first or second inventionto a surface of a substrate to form a thin film of In₂O₃—SnO₂ gelcapable of being crystallized by heat treatment at a temperature of nothigher than 300° C. on the surface of the substrate, and by irradiatingthe thin film with an ultraviolet beam of which wave length is notlonger than 360 nm, the In₂O₃—SnO₂ gel is crystallized, whereby aconductivity is given to the In₂O₃—SnO₂ thin film. At this time, thethin film of In₂O₃—SnO₂ gel formed on the surface of the substrate canbe crystallized by the heat treatment at a temperature of not higherthan 300° C. Accordingly, to crystallize the In₂O₃—SnO₂ gel, it is nomore necessary to perform a heat treatment at a high temperature of 500°C. as is required in the prior arts, and therefore it becomes possibleto form an In₂O₃—SnO₂ thin film on any substrate of low heat resistancesuch as plastics. In addition, mechanism of the crystallization of theIn₂O₃—SnO₂ gel by the irradiation with ultraviolet beam is not alwaysclear, but it is presumed that the thin film absorbs the ultravioletbeam, and rearrangement of atoms takes place by the energy thereof,eventually resulting in the crystallization of the In₂O₃—SnO₂ gel.Accordingly, in the production method according to the third invention,a transparent conductive thin film of In₂O₃—SnO₂ can be formed also onthe substrate of low heat resistance such as plastics.

The fourth invention provides a production method characterized in thatthe In₂O₃—SnO₂ precursor sol obtained by the production method accordingto the mentioned first or second invention is applied to a surface of asubstrate, a thin film of In₂O₃—SnO₂ gel capable of being crystallizedby heat treatment at a temperature of not higher than 300° C. is formedon the surface of the substrate, then the thin film is irradiated withan ultraviolet beam of which wave length is not longer than 260 nm toform a gel film in which fine grains of metallic indium and/or metallictin are dispersed, and the gel film is further irradiated with a laserbeam of which wave length is not longer than 360 nm to crystallize thegel forming the thin film, whereby an In₂O₃—SnO₂ thin film having aconductivity is formed on the surface of the substrate.

In the production method of above composition according to the fourthinvention, by applying the In₂O₃—SnO₂ precursor sol obtained by theproduction method according to the mentioned first or second inventionto a surface of a substrate to form a thin film of In₂O₃—SnO₂ gel, andby irradiating the thin film with an ultraviolet beam of which wavelength is not longer than 360 nm, a gel film in which fine grains ofmetallic indium and/or metallic tin are dispersed can be obtained. Atthis time, the thin film of In₂O₃—SnO₂ gel formed on the surface of thesubstrate can be crystallized by the heat treatment at a temperature ofnot higher than 300° C. Mechanism of the formation of the metallicindium or metallic tin is not always clear, but it is presumed that byirradiating the thin film of In₂O₃—SnO₂ gel with the ultraviolet beam ofwhich wave length is not longer than 260 nm, cleavage of the combinationM—O (metal-oxygen) in the metal oxide proceeds, whereby a reductionproceeds. At the same time, the combination O—C (oxygen-carbon) of theorganic substance remaining in the thin film of In₂O₃—SnO₂ gel is alsocut off. As a result of this, it becomes possible to obtain a gel filmin which amount of residual organic substance is less and fine grains ofmetallic indium and/or metallic tin are dispersed.

Then, when the laser beam of which wave length is not longer than 360 nmis absorbed by the gel film in which fine grains of metallic indiumand/or metallic tin are dispersed, indium and/or tin in the gel film areagain oxidated, whereby the gel film is crystallized. In this case, ifgrain size of the fine grains of the metallic indium and/or metallic tindispersed in the gel film is larger than 100 nm, the metal is left inthe thin film after the irradiation of the gel film with laser beam, andtransmittance of the In₂O₃—SnO₂ thin film is lowered. On the other hand,if grain size of the fine grains of the metallic indium and/or metallictin dispersed in the gel film is not larger than 100 nm, an In₂O₃—SnO₂thin film of high transparency can be obtained.

Accordingly, in the production method according to the fourth invention,the transparent conductive In₂O₃—SnO₂ thin film can be obtained withoutperforming any heat treatment, and an In₂O₃—SnO₂ thin film having aconductivity can be formed on the substrate of low heat resistance suchas plastics. Further, the fourth invention is also applicable to thepatterning of In₂O₃—SnO₂ without step as described later.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a thin film X ray diffraction pattern of the In₂O₃—SnO₂thin film obtained by burning the thin film of In₂O₃—SnO₂ gel formed ona silica glass substrate at a temperature of 300° C.

FIG. 2 is a graph showing a relation between burning temperature of thethin film of In₂O₃—SnO₂ gel obtained by forming a film of In₂O₃—SnO₂precursor sol and film thickness of In₂O₃—SnO₂ thin film.

FIG. 3 shows a thin film X ray diffraction pattern of the In₂O₃—SnO₂thin film obtained by irradiating the thin film of In₂O₃—SnO₂ gelobtained by forming a film of In₂O₃—SnO₂ precursor sol with ArF excimerlaser beam.

FIG. 4 shows a thin film X ray diffraction pattern of the metaldispersed gel film obtained by irradiating the thin film of In₂O₃—SnO₂gel obtained by forming a film of In₂O₃—SnO₂ precursor sol withultraviolet beam using a low pressure mercury lamp.

FIG. 5 is a partially enlarged longitudinal sectional view to explain anexample to which the fourth invention is applied.

FIG. 6 is a partially enlarged longitudinal sectional view showing theconventional patterning of In₂O₃—SnO₂ according to the prior art.

BEST MODE FOR CARRYING OUT THE INVENTION

In the production method of the In₂O₃—SnO₂ precursor sol according toeach of the first and second inventions, indium alkoxide and tinalkoxide are used as starter materials, and a solution containing thesestarter materials are hydrolyzed and polymerized.

In this respect, as a result of repeating various discussions andstudies to obtain an In₂O₃—SnO₂ precursor sol which is capable of beinghighly concentrated and superior in stability and film formationcharacteristic, it was found that the In₂O₃—SnO₂ precursor sol havingrequired characteristics could be obtained by hydrolyzing the solutioncontaining indium alkoxide and tin alkoxide employing eithertri-s-butoxyindium or tri-t-butoxyindiumas the indium alkoxide. Thus,the method according to the first invention is characterized in thateither tri-s-butoxyindium or tri-t-butoxyindium is used as the indiumalkoxide.

As the tin alkoxide, tin propoxide, tin butoxide and tin bentoxide areused, and among which tin butoxide is most suitably used. In particular,when using one tin alkoxide among the tetra-n-butoxytin,tetra-s-butoxytin and tetra-t-butoxytin or using two of them, it ispossible to prepared an In₂O₃—SnO₂ precursor sol which is capable ofbeing highly concentrated and superior in stability and film formationcharacteristic.

Solvent used in the preparation of the In₂O₃—SnO₂ precursor sol is notparticularly defined as far as a reaction product between the mentionedalkoxide and indium alkoxide and the tin alkoxide is soluble, andalcohol, hydrocarbon, aromatic, tetrahydroxyfuran (THF), dioxane,organic acid ester such as methyl acetate, ethyl acetate, acetonitrile,acetone, ketone such as ethyl methyl ketone can be used.

It is preferable that acid amide (RCONR′R″: R, R′ and R″ are alkylgroups) is included in the solution containing alkoxide . It ispreferable that the acid amide is included at a concentration of notless than 5 weight %. As the acid amide, formamide (FA), acetoamide,N-methylformamide, N,N-dimethylformamide, n,n-diethylformamide andN,N-dimethylacetoamide, etc. are used. By including acid amide in thesolution containing alkoxide, the high concentration, stability and filmformation characteristic of the sol are improved. It is also preferablethat β-diketone (RCOCH2COR′: R and R′ are alkyl groups or alkoxylgroups) is included in the solution containing alkoxide. It ispreferable that the β-diketone is included in the amount of 0.1 mol to0.5 mol time as much as the indium alkoxide and tin alkoxide. As theβ-diketone, acetyl acetone, acetoacetic ester such as ethyl acetoacetate(etac), methyl acetoacetate (meac), malonic ester such as diethylmalonate are used. By including β-diketone in the solution containingalkoxide, the β-diketone forms a substitution product of alkoxyl groupof the alkoxide, and the alkoxide is stabilized, whereby the filmformation characteristic of the sol is further improved and morehomogeneous film can be formed.

In the hydrolysis of the solution containing alkoxide, a water of 0.5mol to 2 mol times as much as alkoxide is used and, more preferably, awater of 0.5 mol to 1.5 mol times is used. In this hydrolysis, acidcatalyst and/or base catalyst may be used and, preferably, mineral acidsuch as hydrochloric acid and organic acid such as acetic acid are used.

The method for producing an In₂O₃—SnO₂ precursor sol is characterized inthat indium alkoxide and tin alkoxide are hydrolyzed and polymerized byadding water to a solution containing the indium alkoxide and tinalkoxide at a temperature of not higher than −20° C.

In the method according to the second invention, the indium alkoxide andtin alkoxide to be used are not particularly defined, but from theviewpoint of concentration of oxide contained, easy elimination oforganic substance, easy procurement or availability, etc., it ispreferable to use those of which carbon number of alkoxyl group is 1 to4. For example, as the indium alkoxide, indium methoxide, indiumethoxide, indium propoxide and indium butoxide are used, and among whichtri-i-propoxyindium, tri-s-butoxyindium, tri-t-butoxyindium, etc. arepreferably used. As the tin alkoxide, tin methoxide, tin ethoxide, tinpropoxide and tin butoxide are used, and among which tetra-i-propoxytin,tetra-n-butoxytin, tetra-s-butoxytin, tetra-t-butoxytin, etc. arepreferably used. One of the mentioned indium alkoxides or tin alkoxidesmay be singly used, or two or more of them may be used in combinationwith each other. Ratio of content of indium alkoxide and tin alkoxide isnot particularly defined, but it is preferable to select a ratio inwhich 1 weight % to 20 weight % of SnO₂ is included in In₂O₃—SnO₂ inorder to obtain an In₂O₃—SnO₂ conductive film of lower resistance.

Temperature of adding water to the solution containing indium alkoxideand tin alkoxide depends on the stability of those alkoxide, and thetemperature may be −20° C., and depending on the type of indium alkoxideand tin alkoxide, the it is preferable that addition is performed in thetemperature range of −50° C. to −80° C. By performing the addition ofwater at a low temperature of −20° C., it is possible for the indiumalkoxide and tin alkoxide to perform a hydrolysis and polymerizationreaction at a high concentration without stabilizing the alkoxide byadding any multidentate compound to the indium alkoxide and tinalkoxide, and therefore an In₂O₃—SnO₂ precursor sol of highconcentration not containing any unnecessary organic substance such asmultidentate compound can be obtained. As a result, when using such anIn₂O₃—SnO₂ precursor sol, a gel film containing less organic substanceis easily obtained, and when the organic substance is eliminated fromthe gel through heat treatment or the like, destruction of fineorganization and number of residual pores can be reduced in the obtainedthin film.

Solvent to be used may be a single solvent or a mixed solvent and is notparticularly defined as far as raw material of alkoxide and water usedin the hydrolysis are soluble. For example, it is no problem to combinea polar solvent with an inactive solvent. From the view points ofviscosity, easy removal, etc. in the temperature range for adding water,methanol, ethanol and propanol being an alcohol of which carbon numberis 1 to 3 are preferably used.

To make easy the elimination of the solvent after the gelation, it ispreferable that amount of use of the multidentate compound directlycombined with alkoxide is restrained as much as possible. Instead, inthe method according to the second invention, it is possible to preparethe In₂O₃—SnO₂ precursor sol without using any multidentate compound. Onthe other hand, acid amide or the like represented by RCONR′ (R, R′ arehydrogen or alkyl group) having a plurality of functional groups capableof being coordinated does not form a combination with alkoxyl group bysubstitution, and does not solidify at the temperature of addition ofwater, which means that the acid amide or the like can be easily removedby volatilization and therefore can be used without problem.

Amount of addition of water is different depending on the type of thealkoxyl group in the indium alkoxide and tin alkoxide and on the mixingratio between indium alkoxide and tin alkoxide, and therefore cannot bespecified. Further, depending on the type of alkoxyl group and on themixing ratio between indium alkoxide and tin alkoxide, the optimumstable pH value of sol is different, and therefore any acid or base isappropriately used as a catalyst. The catalyst to be used is notparticularly defined, but to obtain a material of high purity, it ispreferable to use a compound not containing metallic component. Forexample, mineral acid such as hydrochloric acid, nitric acid, sulfuricacid, phosphoric acid, and organic acid such as carbonic acid, boricacid, formic acid, acetic acid, oxalic acid are used as the acid.Ammonia, amine, etc. are used as the base.

Then, in the production method of the In₂O₃—SnO₂ thin film according toeach of the third and fourth inventions, the In₂O₃—SnO₂ precursor solobtained by the production method according to the first or secondinvention is applied to a surface of a substrate, and after drying it, athin film of In₂O₃—SnO₂ gel capable of being crystallized by the heattreatment at a temperature of not higher than 300° C. is formed on thesurface of the substrate. Thereafter, in the method according to thethird invention, the thin film of In₂O₃—SnO₂ gel formed on the surfaceof the substrate is irradiated with an ultraviolet beam of which wavelength is not longer than 360 nm, whereby the In₂O₃—SnO₂ gel forming thethin film is crystallized, and an In₂O₃—SnO₂ thin film having aconductivity is formed on the surface of the substrate. In the fourthinvention, the thin film of In₂O₃—SnO₂ gel formed on the surface of thesubstrate is irradiated with an ultraviolet beam of which wave length isnot longer than 260 nm, and a gel film on which fine grains of metallicindium and/or metallic tin are dispersed is formed, then the gel filmwith metal grains dispersed is irradiated with a laser beam of whichwave length is not longer than 360 nm, whereby the In₂O₃—SnO₂ gelforming the thin film is crystallized, and an In₂O₃—SnO₂ thin filmhaving a conductivity is formed on the surface of the substrate.

The process for applying the In₂O₃—SnO₂ precursor sol to the surface ofthe substrate is not particularly defined, and dip coating, spincoating, flow coating, spray coating, etc. usually employed are used.The thin film of In₂O₃—SnO₂ gel formed on the surface of the substrateat this time can be crystallized at the time of the heat treatment bythe temperature of not higher than 300° C.

When the thin film of In₂O₃—SnO₂ gel is formed on the surface of thesubstrate, in the method according to the third invention, the thin filmis irradiated with an ultraviolet beam of which wave length is notlonger than 360 nm. As the light source of the ultraviolet beam, highpressure mercury lamp, low pressure mercury lamp, excimer lamp, ArFexcimer laser, KrF excimer laser, KrCl excimer laser, XeF excimer laser,synchrotron radiation beam, etc. are used and, more preferably, lowpressure mercury lamp, excimer lamp, ArF excimer laser, KrF excimerlaser or synchrotron radiation beam of which peak wave length is shorteris used. It is also possible to use two or more of these light sourcesin combination. Thus, as a result of irradiating the thin film ofIn₂O₃—SnO₂ gel, the In₂O₃—SnO₂ gel forming the thin film iscrystallized, thereby a conductivity being given to the thin film, and atransparent conductive In₂O₃—SnO₂ thin film is formed on the surface ofthe substrate.

Further, when the thin film of In₂O₃—SnO₂ gel is formed on the surfaceof the substrate, in the method according to the fourth invention, thethin film is irradiated with an ultraviolet beam of which wave length isnot longer than 260 nm. As the light source of the ultraviolet beam, lowpressure mercury lamp, excimer lamp, etc. are used. As a result ofirradiating the thin film of In₂O₃—SnO₂ gel with the ultraviolet beam ofwhich wave length is not longer than 260 nm, a gel film with metallicindium and/or metallic tin dispersed is obtained.

Length of beam irradiation is appropriately decided depending on thetype of liquid applied, ratio between indium and tin, thickness of thethin film of In₂O₃—SnO₂ gel, etc., and to obtain the In₂O₃—SnO₂ thinfilm, it is preferable that transmittance of the metal dispersed gelfilm after the irradiation is not lower than 20%. If the transmittanceof the gel film after the irradiation is lower than 20%, any metalremains after the irradiation of the metal dispersed gel film with alaser beam in the next process, and the transmittance of the In₂O₃—SnO₂thin film is lowered. Therefore, it is more preferable that thetransmittance of the metal dispersed gel film after the irradiation isin the range of 30% to 60%.

When the metal dispersed gel film is formed on the surface of thesubstrate, the gel film is irradiated with a laser beam. In thisprocess, a light source for irradiation of a light of which wave lengthis not longer than 360 nm is used. As the light source, ArF laser (193nm), KrF laser (249 nm), triple wave (353 nm) and quadruple wave (266nm) of YAG laser, etc. are used. It is also possible to use two or moreof these light sources in combination. Thus, as a result of irradiatingthe metal dispersed gel film with the laser beam, indium and/or tin inthe gel film are again oxidized, the gel film is crystallized, whereby atransparent conductive thin film is formed on the surface of thesubstrate.

Described hereinafter are examples to which the invention isspecifically applied.

<Preparation of the In₂O₃—SnO₂ gel>

EXAMPLES 1 TO 26

By hydrolyzing a solution containing indium alkoxide and tin alkoxide ata predetermined ratio so that concentration of solid In₂O₃ and SnO₂ are5 weight %, an In₂O₃—SnO₂ precursor sol was obtained. Type of indiumalkoxide and tin alkoxide, ratio of indium In and tin Sn (SnO₂ weight%), type of solvent, and amount of water used in the hydrolysis areshown in Tables 1 and 2, together with those of Comparative Examples 1to 3 described later. In Tables 1 and 2, “amount” of acid amide is shownin weight %, and “amount” of β-diketone is shown in mol ratio to (In+Sn)“Amount of addition” of “water” is shown in mol ratio of H₂O/(In+Sn),and “pH” of “water” was adjusted by hydrochloric acid (HCl)

TABLE 1 Raw material Solvent Water In-alkoxide Sn-alkoxide SnO2 weight %Acid amide Amount β-diketone Amount Amount of addition pH Example  1In(O-t-C4H9)3 Sn(O-n-C4H9)4 10 DMF 50 acac 0.5 1 1  2 In(O-t-C4H9)3Sn(O-s-C4H9)4 10 DMF 50 acac 0.5 1 1  3 In(O-t-C4H9)3 Sn(O-t-C4H9)4 10DMF 50 acac 0.5 1 1  4 In(O-t-C4H9)3 Sn(O-s-C4H9)4 2 DMF 50 acac 0.5 1 1 5 In(O-t-C4H9)3 Sn(O-s-C4H9)4 5 DMF 50 acac 0.5 1 1  6 In(O-t-C4H9)3Sn(O-s-C4H9)4 15 DMF 50 acac 0.5 1 1  7 In(O-t-C4H9)3 Sn(O-s-C4H9)4 20DMF 50 acac 0.5 1 1  8 In(O-s-C4H9)3 Sn(O-s-C4H9)4 10 DMF 50 acac 0.5 11  9 In(O-t-C4H9)3 Sn(O-s-C4H9)4 10 DMF 5 acac 0.5 1 1 10 In(O-t-C4H9)3Sn(O-s-C4H9)4 10 DMF 20 acac 0.5 1 1 11 In(O-t-C4H9)3 Sn(O-s-C4H9)4 10DMF 90 acac 0.5 1 1 12 In(O-s-C4H9)3 Sn(O-s-C4H9)4 10 DMF 50 acac 0.1 11 13 In(O-s-C4H9)3 Sn(O-s-C4H9)4 10 DMF 50 acac 0.8 1 1 14 In(O-s-C4H9)3Sn(O-s-C4H9)4 10 DMF 50 acac 1 1 1 15 In(O-s-C4H9)3 Sn(O-s-C4H9)4 10 DMF50 acac 1.5 1 1 16 In(O-t-C4H9)3 Sn(O-n-C4H9)4 2 DMF 50 acac 0.5 1 1 17In(O-t-C4H9)3 Sn(O-n-C4H9)4 5 DMF 50 acac 0.5 1 1

TABLE 2 Raw Material Solvent Water In-alkoxide Sn-alkoxide SnO2 weight %Acid amide Amount β-diketone Amount Amount of addition pH 18In(O-t-C4H9)3 Sn(O-n-C4H9)4 15 DMF 50 acac 0.5 1 1 19 In(O-t-C4H9)3Sn(O-n-C4H9)4 20 DMF 50 acac 0.5 1 1 20 In(O-t-C4H9)3 Sn(O-s-C4H9)4 10DMF 50 acac 0.5 1 3 21 In(O-t-C4H9)3 Sn(O-s-C4H9)4 10 DMF 50 acac 0.5 15 22 In(O-t-C4H9)3 Sn(O-s-C4H9)4 10 DMF 50 acac 0.5 0.5 1 23In(O-t-C4H9)3 Sn(O-s-C4H9)4 10 DMF 50 acac 0.5 1.5 1 24 In(O-t-C4H9)3Sn(O-s-C4H9)4 10 DMF 50 meac 0.5 1 1 25 In(O-t-C4H9)3 Sn(O-s-C4H9)4 10DMF 50 etac 0.5 1 1 26 In(O-t-C4H9)3 Sn(O-s-C4H9)4 10 HA 50 acac 0.5 1 1Comparative In(O-n-C3H5)3 Sn(O-s-C4H9)4 10 DMF 50 acac 0.5 1 1 Example 12 In(O-s-C4H9)3 Sn(O-s-C4H9)4 10 DMF 0 acac 0.5 1 1 3 In(O-s-C4H9)3Sn(O-s-C4H9)4 10 DMF 50 acac 0 1 1

Then, after dip coating the obtained In₂O₃—SnO₂ precursor sol on asilica glass substrate, an In₂O₃—SnO₂ gel was crystallized by burning athin film of In₂O₃—SnO₂ gel at a predetermined temperature for one hour.Condition of the In₂O₃—SnO₂ precursor sol obtained in the foregoingexamples, condition of the thin film of In₂O₃—SnO₂ gel after dip coatingon the silica glass substrate, and crystallizing temperature of theIn₂O₃—SnO₂ gel are shown in Table 3 together with the results ofComparative Examples 1 to 3 described later. In Table 3, “◯” in thecolumn of “condition of sol” shows that a transparent homogeneous solwas prepared. “◯” in the column of “condition of film” shows that atransparent homogeneous film was prepared, and “×” shows that any filmwas not formed.

TABLE 3 Crystallization Condition of Sol Condition of Film Temperature(° C.) Example  1 ◯ ◯ 270  2 ◯ ◯ 270  3 ◯ ◯ 270  4 ◯ ◯ 250  5 ◯ ◯ 260  6◯ ◯ 280  7 ◯ ◯ 300  8 ◯ ◯ 270  9 ◯ ◯ 260 10 ◯ ◯ 260 11 ◯ ◯ 280 12 ◯ ◯260 13 ◯ ◯ 270 14 ◯ ◯ 270 15 ◯ ◯ 280 16 ◯ ◯ 250 17 ◯ ◯ 280 18 ◯ ◯ 290 19◯ ◯ 300 20 ◯ ◯ 260 21 ◯ ◯ 250 22 ◯ ◯ 270 23 ◯ ◯ 270 24 ◯ ◯ 270 25 ◯ ◯270 26 ◯ ◯ 270 Comparative Example  1 Precipitation X  450*  2 PartialGelation X  400*  3 Partial Gelation X  420*

As is obviously understood from the results shown in Table 3, atransparent In₂O₃—SnO₂ precursor sol was obtained in every group ofExamples 1 to 26 according to the first invention, and there was noproblem at all in the film formation characteristic. A crystal phase ofIn₂O₃—SnO₂ was acknowledged at a temperature of 250 to 300° C. There wasa tendency that when more tin was added and more DMF was added, thecrystallization temperature was higher. Further, as a result of detailedanalysis of the crystallization starting temperature in Example 3, acrystal phase was acknowledged by burning at a temperature of 230° C.for 12 hours. FIG. 1 shows a thin film X ray diffraction pattern of theIn₂O₃—SnO₂ thin film obtained by burning the thin film of In₂O₃—SnO₂ gelformed on a silica glass substrate at a temperature of 300° C. inExample 3.

Comparative Examples 1 to 3

An In₂O₃—SnO₂ precursor sol was prepared in the composition shown inTable 1. As is understood from the results shown in Table 3, anyhomogeneous In₂O₃—SnO₂ precursor sol could not obtained. Crystallizationtemperature was inspected by drying and heat treating the precipitateand gelated substance, and it was found that the crystallizationtemperature was so high as to be 400 to 420° C. as compared with theexamples according to the first invention.

<Preparation of thin film of In₂O₃—SnO₂ gel>

EXAMPLES 27 TO 42

Indium alkoxide and tin alkoxide were added to ethanol so thatconcentration of solid In₂O₃ and SnO₂ was 15 weight %, thus a mixedsolution of indium alkoxide and tin alkoxide was prepared. Then a mixedsolution of distilled water-ethanol was prepared so that concentrationof solid In₂O₃ and SnO₂ was 10 weight % when added to the mixed solutionof alkoxide. After cooling the mixed solution of alkoxide and the mixedsolution of distilled water-ethanol to a predetermined temperature in arefrigerant, the two solutions were mixed and, thereafter, the mixedsolution was returned to room temperature, whereby a homogeneousIn₂O₃—SnO₂ precursor sol was obtained. Mixing ratio and compositionconditions are shown in Table 4 together with those of ComparativeExamples 4 and 5 described later. In Table 4, “Amount of addition” of“water” is shown in mol ratio of H₂O/(In+Sn), and “pH” of “water” wasadjusted by hydrochloric acid (HCl). In Table 4, “◯” in the column of“condition of film” shows that a transparent homogeneous film wasprepared.

TABLE 4 Raw Material Water Temperature of Condition In-alkoxideSn-alkoxide SnO2 weight % Solvent Amount of addition pH Addition (° C.)of Sol Example 27 In(O-s-C4H9)3 Sn(OC2H5)4 10 ethanol 0.6 1 −75 ◯ 28In(O-s-C4H9)3 Sn(O-n-C3H7)4 10 ethanol 0.6 1 −75 ◯ 29 In(O-s-C4H9)3Sn(O-i-C3H7)4 10 ethanol 0.6 1 −75 ◯ 30 In(O-s-C4H9)3 Sn(O-n-C4H9)4 10ethanol 0.6 1 −75 ◯ 31 In(O-s-C4H9)3 Sn(O-s-C4H9)4 10 ethanol 0.6 1 −75◯ 32 In(O-s-C4H9)3 Sn(O-t-C4H9)4 10 ethanol 0.6 1 −75 ◯ 33 In(O-s-C4H9)3Sn(O-s-C4H9)4 2 ethanol 0.6 1 −75 ◯ 34 In(O-s-C4H9)3 Sn(O-s-C4H9)4 5ethanol 0.6 1 −75 ◯ 35 In(O-s-C4H9)3 Sn(O-s-C4H9)4 15 ethanol 0.6 1 −75◯ 36 In(O-s-C4H9)3 Sn(O-s-C4H9)4 20 ethanol 0.6 1 −75 ◯ 37 In(O-s-C4H9)3Sn(O-s-C4H9)4 10 ethanol 0.6 3 −75 ◯ 38 In(O-s-C4H9)3 Sn(O-s-C4H9)4 10ethanol 0.6 5 −75 ◯ 39 In(O-s-C4H9)3 Sn(O-s-C4H9)4 10 dimethyl 0.6 1 −50◯ formaldehyde 40 In(O-s-C4H9)3 Sn(O-s-C4H9)4 10 ethanol 0.6 1 −75 ◯ 41In(O-i-C3H7)3 Sn(O-s-C4H9)4 10 ethanol 0.6 1 −75 ◯ 42 In(O-i-C3H7)3Sn(O-i-C3H7)4 10 ethanol/2- 0.6 1 −75 ◯ propanol Comparative Example  4In(O-t-C4H9)3 Sn(O-s-C4H9)4 10 ethanol 0.6 1 Room Partial TemperatureGelation  5 In(O-t-C4H9)3 Sn(O-s-C4H9)4 10 2-butanol 1 1 Room ◯Temperature

Then, the obtained In₂O₃—SnO₂ precursor sol was diluted so thatconcentration of oxides of respective In₂O₃ and SnO₂ was 5 weight %, andthe diluted sol was spin coated at a revolution of 1,000 rpm, whereby afilm was formed on a silica substrate. Thus, an apparently homogeneousthin film of In₂O₃—SnO₂ gel was obtained. The obtained thin film wasburned at a predetermined temperature for one hour, and the In₂O₃—SnO₂gel was crystallized. A transparent In₂O₃—SnO₂ precursor sol wasobtained in every group of Examples 27 to 42 according to the secondinvention, and there was no problem at all in the film formationcharacteristic. A crystal phase of In₂O₃—SnO₂ was acknowledged at atemperature of 250 to 300° C. In the same manner as the foregoingExamples 1 to 26, there was a tendency that when more tin was added andmore DMF was added, the crystallization temperature was higher.

Further, film thickness and resistance value of the In₂O₃—SnO₂ thin filmafter the heat treatment was measured and evaluated. Film thickness wasmeasured using a step measuring meter. Resistance value was obtained by4 terminal method (In the measurement, Rolester·MP, MCP-T-350 producedby Mitsubishi Chemical was used). Characteristics of the obtained filmwas shown in FIG. 5 together with those of Comparative Example 5described later.

TABLE 5 Sheet Specific Burning Film Resistance Resistance SolTemperature Thickness (nm) (Ω/□) (Ω cm) Example 27 400 70 3.60E + 032.52E − 02 28 400 75 3.20E + 03 2.40E − 02 29 400 75 3.60E + 03 2.70E −02 30 400 80 3.10E + 03 2.48E − 02 31 400 85 2.50E + 03 2.13E − 02 31500 80 7.40E + 02 5.92E − 03 32 400 85 2.70E + 03 2.30E − 02 33 400 854.80E + 04 4.08E − 01 34 400 80 4.10E + 03 3.28E − 02 35 400 80 2.30E +03 1.84E − 02 36 400 75 2.80E + 03 2.10E − 02 37 400 75 2.90E + 03 2.18E− 02 38 400 90 2.70E + 03 2.43E − 02 39 400 65 4.10E + 03 2.67E − 02 40400 90 2.60E + 03 2.34E − 02 Comparative Example  5 500 40 8.30E + 033.32E − 02

Comparative Example 4

Tri-t-butoxyindium and tetra-s-botoxytin were added to ethanol so thatconcentration of solid In₂O₃ and SnO₂ was 5 weight %, thus a mixedsolution of alkoxide was prepared. Then a mixed solution of INhydrochloric acid-ethanol (mol ratio of H₂O/(In+Sn) is 0.6) was preparedso that concentration of solid oxide was 2.5 weight % when added to themixed solution of alkoxide, and this mixed solution was added to themixed solution of alkoxide at room temperature. Any homogeneous solcould not obtained because of partial opaqueness ad gelation startingfrom the portion where water (IN hydrochloric acid-ethanol) was added.

Comparative Example 5

Tri-t-butoxyindium and tetra-s-botoxytin were added to 2-butanol so thatconcentration of solid In₂O₃ and SnO₂ was 5 weight %, thus a mixedsolution of alkoxide was prepared. Then a mixed solution of INhydrochloric acid-2-butanol (mol ratio of H₂O/(In+Sn) is 1) was preparedso that concentration of solid oxide was 2.5 weight % when added to themixed solution of alkoxide. After adding acetyl acetone equimolar toindium alkoxide and tin alkoxide to the mixed solution, the mixedsolution of IN hydrochloric acid-2-butanol was added to the mixedsolution of alkoxide at room temperature. A homogeneous solution wasobtained when concentration of the solid oxide was not higher than 2.5weight %, but a partial opaqueness was found when the concentration wasnot lower than 3 weight %. The obtained sol was formed into a film inthe same manner as Examples 27 to 40.

As is explicit from the mentioned results, in the production methodaccording to the second invention, it is possible to obtain ahomogeneous sol in which concentration of In₂O₃—SnO₂ was not lower than10 weight % without adding any organic substance such as multidentatecompound. On the contrary, in the conventional method, it is certainlypossible to prepare a partially stable sol by adding a multidentatecompound, but concentration of oxide thereof is low.

Further, as is understood from the results shown in Table 5, there is atendency that film thickness of the In₂O₃—SnO₂ thin film produced by themethod of Examples 27 to 42 according to the second invention is large,sheet resistance is small, and specific resistance value is small, ascompared with those of Comparative Examples 4 and 5. This is, perhaps,because in the film produced according to the second invention, residualorganic component is small, and accordingly defect such as pores in theinternal part of the film is reduced.

Further, with respect to the In₂O₃—SnO₂ precursor sol obtained inExample 34, variation in film thickness of the In₂O₃—SnO₂ thin film inassociation with the change in burning temperature was inspected whenthe thin film of In₂O₃—SnO₂ gel obtained by forming the film in the samemanner as mentioned above was burned at various temperatures. Further,from the viewpoint of comparison, with respect to the In₂O₃—SnO₂precursor sol obtained i n Comparative Example 5, a relation betweenburning temperature of the thin film thickness of In₂O₃—SnO₂ gel and thefilm thickness of the obtained In₂O₃—SnO₂ thin film was inspected. FIG.2 shows the results. In FIG. 2, a curve I indicates the result of thethin film of In₂O₃—SnO₂ gel obtained by forming the In₂O₃—SnO₂ precursorsol obtained in Example 34 into the film, and another curve II indicatesthe result of the thin film of In₂O₃—SnO₂ gel obtained by forming theIn₂O₃—SnO₂ precursor sol obtained in Comparative Example 5 into thefilm.

As shown in FIG. 2, it was acknowledged that in the thin film ofIn₂O₃—SnO₂ gel obtained by forming the In₂O₃—SnO₂ precursor sol obtainedin Example 34 into the film, ratio of shrinkage due to the burning wasabout 40%, while in the thin film of In₂O₃—SnO₂ gel obtained by formingthe In₂O₃—SnO₂ precursor sol obtained in Comparative Example 5 into thefilm, ratio of shrinkage due to the burning mounted to about 65%.Accordingly, it is understood that if the thickness of the thin film ofIn₂O₃—SnO₂ gel is equal, film thickness of the In₂O₃—SnO₂ thin filmobtained by the method according to the second invention is large ascompared with the In₂O₃—SnO₂ thin film obtained by the conventionalmethod.

Further, the In₂O₃—SnO₂ precursor sol obtained in Example 34 was dilutedso that concentration of oxide is 5 weight %, and the diluted sol isformed into a film by dip coating, and the same evaluation as mentionedabove was performed. By burning the obtained thin film of In₂O₃—SnO₂ gelat a temperature of 400° C., an In₂O₃—SnO₂ thin film of 85 nm in filmthickness and 2.6×10³ Ω/□ in sheet resistance was obtained. TheIn₂O₃—SnO₂ precursor sol obtained in Example 34 was also diluted so thatconcentration of oxide is 1 weight %, and the diluted sol is formed intoa film by flow coating on a glass substrate of 50 mm square, whereby athin film of homogeneous In₂O₃—SnO₂ gel was obtained with out problem.By burning the obtained thin film of In₂O₃—SnO₂ gel at a temperature of400° C., an In₂O₃—SnO₂ thin film of 65 nm in film thickness and 3.6×10³Ω/□ in sheet resistance was obtained.

<Crystallization by Irradiation with Ultraviolet Beam>

EXAMPLE 43

Using the In₂O₃—SnO₂ precursor sol of the foregoing Example 1 and spincoating this sol at a revolution of 1,000 rpm, a film was formed on asilica substrate. The obtained thin film of In₂O₃—SnO₂ gel wasirradiated with ArF excimer laser beam (193 nm, 20 mJ/cm²) by 100 shots.As a result, a crystallization of In₂O₃—SnO₂ phase was acknowledged bythin film X ray diffraction as shown in FIG. 3. This thin film X raydiffraction pattern was the same pattern as the X ray diffractionpattern of the In₂O₃—SnO₂ thin film obtained by heating and shown inFIG. 1, and therefore in the method according to the third invention, itis possible to produce a crystalline conductive In₂O₃—SnO₂ thin film atroom temperature without heat treatment. In the obtained crystallineIn₂O₃—SnO₂ thin film, specific resistance was 4.6×10⁻³ Ωcm andtransmittance with respect to a light of 520 nm in wave length was 90%.

EXAMPLE 44

Using the In₂O₃—SnO₂ precursor sol of the foregoing Example 31 and spincoating this sol at a revolution of 1,000 rpm, a film was formed on asilica substrate. The obtained thin film of In₂O₃—SnO₂ gel wasirradiated with ArF excimer laser beam (193 nm, 20 mJ/cm²) by 100 shots.As a result, a crystallization of In₂O₃—SnO₂ phase was acknowledged bythin film X ray diffraction. In the obtained crystalline In₂O₃—SnO₂ thinfilm, specific resistance was 3×10⁻³ Ωcm and transmittance with respectto a light of 520 nm in wave length was 90%.

EXAMPLE 45

Using the In₂O₃—SnO₂ precursor sol of the foregoing Example 31, a filmwas formed on a PET (polyethyleneterephthalate) substrate, and theobtained thin film of In₂O₃—SnO₂ gel was irradiated with ArF excimerlaser beam on the same conditions as the foregoing Example 44. As aresult, a diffraction peak corresponding to (222) side of In₂O₃—SnO₂ wasobserved and crystallization of In₂O₃—SnO₂ phase was acknowledged. Sheetresistance value of the obtained In₂O₃—SnO₂ thin film was 1.2×10⁴ Ω/□.

As described above, in all of the thin films of In₂O₃—SnO₂ gel obtainedby using the In₂O₃—SnO₂ precursor sol prepared in Examples 1 to 42, theIn₂O₃—SnO₂ phase was crystallized by irradiation with ArF excimer laserbeam, and a conductivity was manifested. Further, it became alsopossible to form a crystalline conductive In₂O₃—SnO₂ thin film on theplastic substrate of low heat resistance such as PET.

<Crystallization by Irradiation with Ultraviolet Beam and by Irradiationwith Laser Beam>

EXAMPLE 46

The thin film of In₂O₃—SnO₂ gel obtained in the foregoing Example 43 wasirradiated with an ultraviolet beam (254 nm, 10 mJ/cm³) at a positionseparated by 3 cm from the light source using a low pressure mercurylamp of 110 W for 3 hours.

By the irradiation with the ultraviolet beam, the thin film ofIn₂O₃—SnO₂ gel on the silica glass substrate was blackened, andtransmittance of the gel film with respect to the light of 550 nm inwave length was 32%. In the obtained gel film, a production of metallicindium and metallic tin was acknowledged by thin film X ray diffraction.In FIG. 4, other than the diffraction pattern of (the thin film ofIn₂O₃—SnO₂ gel) by the irradiation for 3 hours with the ultraviolet beamusing the low pressure mercury lamp, those of the irradiation for 0hour, 1 hour, 6 hours and 12 hours are also shown. In the drawing, thethin film X ray diffraction patterns of the gel films irradiated for 0hour, 1 hour, 3 hours, 6 hours and 12 hours are respectively shown fromthe bottom in order. Further, as a result of observation by transmissiontype electron microscope (TEM), grain size of the metallic indium seenas a high brightness portion was 10 nm to 20 nm.

Further, the obtained metal dispersed gel film was irradiated with anArF excimer laser beam (266 nm, 10 mJ/cm³) by 200 shots, whereby acrystalline In₂O₃—SnO₂ thin film was obtained in the same manner as theforegoing Example 43. In the obtained crystalline In₂O₃—SnO₂ thin film,specific resistance was 4.1×10⁻³ Ωcm and transmittance with respect to alight of 520 nm in wave length was 95%.

EXAMPLE 47

The metal dispersed gel film obtained in the foregoing Example 46 wasirradiated with a KrF excimer laser beam (248 nm, 35 mJ/cm³) by 100shots, whereby a crystalline In₂O₃—SnO₂ thin film was obtained in thesame manner as the foregoing Example 43. In the obtained crystallineIn₂O₃—SnO₂ thin film, specific resistance was 4.2×10⁻³ Ωcm andtransmittance with respect to a light of 520 nm in wave length was 95%.

EXAMPLE 48

The metal dispersed gel film obtained in the foregoing Example 46 wasirradiated with quadruple wave (266 nm) of YAG laser (266 nm, 10 mJ/cm³)by 100 shots. As a result, a diffraction peak corresponding to (222)side of In₂O₃—SnO₂ was observed and crystallization of In₂O₃—SnO₂ phasewas acknowledged. Conductivity was also acknowledged in the obtainedIn₂O₃—SnO₂ thin film.

EXAMPLE 49

The thin film of In₂O₃—SnO₂ gel obtained in the foregoing Example 44 wasirradiated with an ultraviolet beam for three hours using a low pressuremercury lamp on the same conditions as Example 46. By the irradiationwith the ultraviolet beam, the thin film of In₂O₃—SnO₂ gel on the silicaglass substrate was blackened, and a gel film in which grains ofmetallic indium and metallic tin are dispersed was obtained.

The obtained metal dispersed gel film was irradiated with an ArF excimerlaser beam (248 nm, 35 mJ/cm³) by 100 shots, whereby a crystallineIn₂O₃—SnO₂ thin film was obtained in the same manner as the foregoingExample 44. In the obtained crystalline In₂O₃—SnO₂ thin film, specificresistance was 2.1 ×10⁻³ Ωcm and transmittance with respect to a lightof 520 nm in wave length was 95%.

EXAMPLE 50

The metal dispersed gel film obtained in the foregoing Example 49 wasirradiated with a KrF excimer laser beam (248 nm, 35 mJ/cm³) by 100shots, whereby a crystalline In₂O₃—SnO₂ thin film was obtained in thesame manner as the foregoing Example 44. In the obtained crystallineIn₂O3—SnO₂ thin film, specific resistance was 2.2×10⁻³ Ωcm andtransmittance with respect to a light of 520 nm in wave length was 95%.

EXAMPLE 51

The metal dispersed gel film obtained in the foregoing Example 49 wasirradiated with quadruple wave (266 nm) of YAG laser (266 nm, 10 mJ/cm³)by 100 shots. As a result, a diffraction peak corresponding to (222)side of In₂O₃—SnO₂ was observed and crystallization of In₂O₃—SnO₂ phasewas acknowledged. Conductivity was also acknowledged in the obtainedIn₂O₃—SnO₂ thin film.

As described in Examples 46 to 51, by performing a pretreatment using alow pressure mercury lamp, a conductive In₂O₃—SnO₂ thin film ofsatisfactory transmittance as compared with the In₂O₃—SnO₂ thin filmobtained in Examples 43 to 45 was obtained.

EXAMPLE 52

After forming a thin film 2 of In₂O₃—SnO₂ gel on a silica glasssubstrate according to the operation in the foregoing Example 43 asshown in the partially enlarged longitudinal sectional view of FIG.5(a), the thin film 2 of In₂O₃—SnO₂ gel was irradiated with anultraviolet beam 3 as shown in FIG. 5(b), and an obtained metaldispersed gel film 4 was irradiated an ArF excimer laser beam 6 througha photomask 5 for patterning as shown in FIG. 5(c). As a result, asshown in FIG. 5(d), only a portion 7 irradiated with the laser beam 6became transparent, thus a thin film 9 in which conductive In₂O₃—SnO₂was patterned was obtained. Further, by heat treating the thin film 8 ata temperature of 180° C. for 24 hours, a thin film 10 in which a portion9 not irradiated with the laser beam was also transparent was obtained.However, any conductivity was not manifested in the portion 9 of thethin film 10 not irradiated with the laser beam.

In the conventional method for forming the In₂O₃—SnO₂ thin film, asshown in the partially enlarged longitudinal sectional view of FIG. 6,only the patterning of In₂O₃—SnO₂ 11 having steps on the silica glasssubstrate 1 can be performed. On the contrary, when applying the methodaccording to the fourth invention, a patterning of In₂O₃—SnO₂ having nostep became possible as shown in FIG. 5(e).

The patterning method described in this Example 52 was proved applicableto all of the In₂O₃—SnO₂ precursor sol obtained in the foregoingExamples 1 to 42. Though the metal dispersed gel film 4 was irradiatedwith the ArF excimer laser beam 6 in Example 52, the patterning methodshown in Example 52 was found applicable also when irradiated with KrFexcimer laser or quadruple wave of YAG laser.

In addition, the metal dispersed gel films obtained in Examples 46 and49 can be utilized as black mask, etc.

INDUSTRIAL APPLICABILITY

THE PRODUCTION METHOD OF In₂O₃—SnO₂ precursor sol according to thepresent invention is applied to the formation of transparent conductivethin film on the surface of a substrate of glass, ceramics, plastics,etc. and, in particular, in the invention, a transparent conductive thinfilm can be formed also on the surface of a plastic substrate of lessheat resistance.

What is claimed is:
 1. A method for producing an In₂O₃—SnO₂ precursorsol by hydrolyzing and polymerizing a solution containing indiumalkoxide and tin alkoxide, characterized in that water is added to thesolution containing indium alkoxide and tin alkoxide at a temperature ofnot higher than −20° C.
 2. A method for producing an In₂O₃—SnO₂precursor sol according to claim 1, wherein the solution containingindium alkoxide and tin alkoxide is hydrolyzed and polymerized withoutusing any multidentate compound.
 3. A method for producing an In₂O₃—SnO₂precursor sol according to claim 1, wherein the addition of water to thesolution containing indium alkoxide and tin alkoxide is performed withinthe temperature range of −50° C. to −80° C.